The present document is based on Japanese Priority Document JP2001-234143, filed in the Japanese Patent Office on Aug. 1, 2001, the entire contents of which being incorporated herein by reference.
1. Field of the Invention
The present invention relates to an inductor element formed on a plane mounted on an integrated circuit used for an electronic apparatus such as a mobile communications apparatus for example, and yet, the present invention also relates to an integrated circuit employing the inductor element of the present invention.
2. Description of the Related Art
Conventionally, an inductor element is formed on a plane inside of a semiconductor integrated circuit so that aimed circuits can be formed thereon. Taking an amplifier 100 formed as a semiconductor integrated circuit shown in FIG. 1 for example, a pair of inductor elements 103 and 104 is respectively employed for a pair of matching circuits 101 and 102 constituting a part of this amplifier 100.
In order to properly maintain characteristics of the amplifier and save power consumption thereof, it is essential for the above inductor elements 103 and 104 to exhibit smaller loss. In other words, the inductor elements 103 and 104 are individually required to have a higher Q value.
For example, the Japanese Patent Application Publication Laid-Open No. 2000-357774 discloses an inductor element employed in for such a semiconductor integrated circuit as cited above. The inductor element disclosed in the above-cited patent publication is formed with a pair of conductors 111 and 112 aligned in parallel to each other on an substrate as shown in FIG. 2 for example, where a pair of conductors are connected together at terminals 114 and 115.
Focusing on the skin effect in which density of high-frequency current flowing through conductor is intense at a surface of the conductor, by applying a plurality of conductors such as a pair of conductors 111 and 112 for example, it is so arranged that the inductor element shown in FIG. 2 can decrease high frequency resistance inside of these conductors.
Nevertheless, as shown in FIG. 2, in the case of forming an inductance element by helically winding a plurality of conductors aligned in parallel to each other repeatedly in the same direction, length of the outer conductors becomes longer than the inner conductors. The longer the length of conductors, the higher the high-frequency resistance of those outer conductors. Accordingly, current flowing through the first conductor 111 positioned outside decreases.
FIG. 3 shows a result of an analytical simulation on the electromagnetic field of the inductor element shown in FIG. 2. Length of an arrow mark on the first conductor 111 and the second conductor 112 shown in FIG. 3 represents current density.
As shown in FIG. 3, length of the arrow mark designating current density shown in the first conductor 111 positioned outer side is mostly shorter than the arrow mark designating current density shown on the adjoining second conductor 112 positioned inner side. This clarifies that a less amount of current flows through the first conductor than that flows through the second conductor.
Accordingly, in the case of the inductance elements as shown in FIGS. 2 and 3, although a pair of conductors are employed, neither of these can fully exert the effect of decreasing high-frequency resistance, and consequently, power consumption by an integrated circuit employing the above inductor element increases.
Accordingly, the present invention provides an inductor element capable of decreasing high-frequency resistance and loss and preserving a high Q value, and yet, also provides an integrated circuit formed by employing the inductor element of the present invention.
The present invention provides an inductor element comprising a plurality of conductors which are formed in mutually parallel relationship and helically wound within a plane on a surface of a substrate, which is employed as a high-frequency path to enable high-frequency current of an identical phase to flow through the plurality of conductors. By way of crossing the plurality of conductors at a predetermined position, inner positions and outer positions of the plurality of conductors are inverted from each other. The predetermined position is so selected that individual length of the plurality of conductors can become substantially equal to each other.
According to the present invention, by way of substantially equalizing individual length of a plurality of conductors, resistance value of these plural conductors is substantially equalized. Therefore, it is made possible to equalize density of current flowing through the plurality of conductors as much as possible. By virtue of this arrangement, it is possible to realize such an inductor element featuring least loss, high Q value, and satisfactory physical characteristics. Such an inductor element realized by the present invention is suitable for application to an integrated circuit.